Satellites typically have an orbit-raising (“OR”) propulsion system, and an attitude control system (“ACS”). A main rocket motor using liquid bipropellants (i.e., a fuel and an oxidizer) is commonly used to provide major position and velocity changes, such as the raising of a satellite into a desired orbit. It is also known to selectively dispense a stored gas propellant through the thrusters to alter the in-flight attitude of the vehicle. It is further known to use a volatile liquid (e.g., ammonia), having a liquid phase and a gaseous phase, to pressurize the bipropellants.
It would be desirable to reduce the amount of structure and weight in a launchable vehicle. A rule of thumb is that such a vehicle costs $5,000 per kilogram to build, and $10,000 per kilogram to launch.
It would also be generally desirable to provide an improved propulsion system that is of low cost; that is structurally simple; that is lightweight and compact; and that has a substantially fixed center of gravity, even as propellants are dispensed.